Altazimuth Pavilion

Closures: The Altazimuth Pavilion may occasionally be closed. Please see Latest visitor information for details of all closures.

The Altazimuth Pavillion, situated in the Planetarium courtyard, and Onion Dome, Royal Observatory, Greenwich. Repro ID: D3161-1 ©National Maritime Museum, Greenwich, LondonThe Altazimuth Pavilion was built in 1899. It was originally intended to house instruments used to measure the two coordinates used to fix the position of a celestial body in the sky: the altitude (its position above the horizon) and the azimuth (its position east along the horizon), and it is from this coordinate system that it gets its name.

The ground floor of the building contains a small exhibition on the Sun, which is open daily. The upper floor under the dome contains two historic instruments used by the Solar Department at the Royal Observatory until 1949, and is only accessible for special talks and observing events on specific dates throughout the year. The instruments currently housed in the dome include the Newbegin 6.25-inch Refractor and the historic Dallmeyer No.2 Photoheliograph.

About photoheliographs

The Dallmeyer No.3 Photoheliograph, in use at the Royal Observatory, Greenwich until 1910. Repro ID: B1636-17A ©National Maritime Museum, Greenwich, London. Purchased from the RGO in 1980A photoheliograph is a type of telescope made for photographing the Sun. The Dallmeyer No.3 Photoheliograph was originally commissioned in 1871 as one of five photoheliographs ordered from the maker Thomas Rudolphus Dallmeyer, son of John Henry Dallmeyer, for the British expeditions (organised by the Royal Observatory, Greenwich) to view the Transit of Venus in 1874.

All five telescopes were erected at Greenwich in portable observatories in 1873, and in July 1873 one was used for the start of a series of daily photographs of the Sun.

The five photoheliographs were packed and shipped in 1874 to take part in the Transit of Venus expeditions. During that period, a photoheliograph from the Kew Observatory was used to continue the Greenwich daily photographic series.

Dallmeyer No.2 was mounted in the Altazimuth Pavilion in 1911, and was used for observations during the Second World War. It was also used to take the last photograph of the Sun for scientific purposes at the Royal Observatory, Greenwich, on 2 May 1949. On the same day the instrument was mounted on the Newbegin 6.25-inch refracting telescope (AST0929), and both were used regularly until sold to the National Maritime Museum in 1980.